This invention relates to a vented syringe and more particularly to such a syringe useful in obtaining a specimen of blood from an artery for use in blood gas analysis.
For many years the medical profession has used the blood gas test as a useful tool in making diagnostic determinations, particularly with respect to a patient's respiratory or metabolic functions. The blood upon which a blood gas test is performed is normally obtained from the artery of the patient. typically, this is done with a special type syringe which can be preset to a desired amount such as 2 or 3 cubic centimeters. The needle attached to the syringe is inserted into the artery and, normally, blood pressure forces the blood into the preset specimen chamber portion of the syringe. In order to allow the blood to flow into the syringe the piston portion of the syringe must be vented to allow the air displaced by the entering blood to escape. For example, see U.S. Pat. No. 3,674,181 to Marks et al, U.S. Pat. No. 4,299,238 to Baldwan et al. and U.S. Pat. No. 4,361,155 to Anastasio.
By venting the plunger to allow the air to escape as the blood enters the specimen chamber, a path also exists for blood to escape from the chamber and to spill into the surrounding area outside the specimen chamber. The blood spill is not only messy, but also is unhealthy to the technician drawing the blood. One attempt to solve this problem in the past has been the insertion of a membrane designed to pass air, but not liquid (e.g. blood) into the air passage. For example, see U.S. Pat. No. 4,466,446 to Baldwin et al., U.S. Pat. No. 4,373,535 to Hartell, U.S. Pat. No. 4,340,067 to Rettenborg and U.S. Pat. No. 4,327,745 to Ford, Jr. However, experience has shown that blood still leaks through the membrane causing potential contamination to the technician drawing the blood.
In certain instances, the patient's blood pressure is insufficient to pump the blood into the specimen chamber. For these type of patients it is necessary to have a blood gas syringe which can aspirate the blood after the needle is inserted into the artery. The syringes of the prior art which have either an air vent through the piston and/or the membrane typically cannot be used to aspirate the patient's blood. In some instances, such as in U.S. Pat. No. 4,361,155 to Anastasio, the air vent has been connected through a hole in the plunger handle which hole can be covered by the technician's finger and used to aspirate. However, this is inconvenient and not entirely satisfactory because it causes the technician to hold the syringe in an unnatural position, thereby potentially causing the needle to move and damage to the patient's arteries. Other prior art syringes have solved this aspiration problem by allowing a complex mechanism which can be twisted to close the air vent. For example, see U.S. Pat. No. 4,326,540 to Bailey et a. Such devices however require special parts with tight precision requirements in order to be operative, and also result in potential damage to the patient. Other solutions to the problem of being able to aspirate using a blood gas syringe include providing a check valve above the air vent. For example, see U.S. Pat. No. 4,373,535 to Martell. This prior art solution has required special parts, thereby increasing the cost, and did not solve the other problems mentioned above.
Syringes generally are made in large numbers for many medical applications including injecting medicine and aspirating blood. Because of the large numbers of conventional syringes manufactured, the individual components can be inexpensively obtained. It would be of great economic advantage to utilize currently available components in fabricating a syringe which can be used to obtain a blood sample for blood gas analysis.